There can be a considerable amount of information associated with an output image that has been digitally processed and produced on a print by an image processing device. Exemplary types of such information is provided hereinbelow. It is beneficial to have this information integrally coupled to a print and, therefore, readily available for access. This is particularly true for high-quality image prints such as those produced by a digital proofing system, an example of which is the “APPROVAL PS Digital Color Proofing System”™ or “APPROVAL XP/XP4 Digital Proofing System”™ available from the Eastman Kodak Company, located in Rochester, N.Y.
A substantial amount of information can be associated with a print from an imaging system such as a digital proofing system. Output prints from such a system serve as proofs, intended to closely emulate the appearance of a printed output page from a printing press. For a print from such a halftone digital proofing system, because such a system is designed to emulate printing press output, it is important to know the exact conditions under which an image was processed and will be printed. Variables such as dot shape, screen angle, screen ruling, densities of component colors, and dot gain adjustments can be modified for images printed from such systems, depending on corresponding characteristics of the target multi-color printing system that the proofing system is intended to emulate. Because an image is prepared before printing using any one of a number of digital prepress systems (such as for initial scanning, color correction, and imposition), it is also beneficial to identify the specific system or systems on which an image has been processed. It is also useful to identify a filename associated with the image that is reproduced.
For such a proofing system, an image on an output print is carefully analyzed for its overall appearance and color content. Adjustments for improving appearance and color are made based on appearance and color as they appear in the output print. Ideally, a prepress proof is even expected to represent potential problem conditions, such as possible moiré pattern or other imaging anomalies. In practice, the output print from such a system is often used to obtain formal customer approval before an expensive multi-color printing operation is initiated. As part of the requirements for customer approval, it can be important to validate the source of proof data and to identify the precise processing systems and steps employed with this data. This is because the same image data that is used to create a color separation on the digital proof may be used subsequently to produce a printing plate for that same color separation. In fact, in some printing environments, it can be a requirement that the same data used to generate a proof be used to generate a printing plate. It is instructive to note that this same data may be conditioned, that is, the data may be with or without adjustments for known characteristics of an apparatus or output media. For example, different dot gain compensation may be applied to the data when imaged on different devices. Viewed from this perspective, the output print used as a digital proof supports the workflow of a print job during prepress processing stages and through final approval and printing.
For an output print produced from such a digital proofing system, there can be numerous variables associated with the print. With the KODAK APPROVAL PS or XP/XP4 Digital Proofing System noted hereinabove, for example, special Raster Image Processing (or RIP) setup software prompts an operator to enter desired values for screen ruling, screen angles, halftone dot shape, target densities, dot gain characteristics, and other emulation variables. RIP setup software then generates a separate file containing such proofing variables, where this RIP setup file is associated with the image file to be printed.
Thus, considering the overall value of an output print produced on a halftone digital proofing system and considering the complexity of processing and providing such a print to emulate a printing press, it is desirable to couple identifying and processing information to the print. This would be particularly desirable where a print job may be prepared and printed in different locations. For example, prepress work for a periodical may be performed in the State of New York, while final plate preparation and printing take place in the State of California. Under such conditions, image content for a proof may be transmitted electronically from one site to another. It would be useful to provide some method for validating the image source, processing steps, and RIP setup conditions used to prepare a proof, so that the same proof could be readily reproduced, with all desired proofing parameters, at a number of different locations. It would also be useful to authenticate a print, or to provide a method for quickly verifying that two image files are identical, using a form of hash encoding or “digital signature” that is readily accessible on the print itself. Such a method would be especially useful for digital proofing applications, because two proofs could appear identical to the unaided eye, but differ because they were produced with different dot shapes, screen angles, or other variable parameters. Data transmission errors could also cause problems, unless detected using an authentication scheme.
In the information processing arts, information about data, for example information identifying a data source and identifying processing steps carried out on the data, is termed “metadata”. For the digital prepress proofing application described above, metadata for the actual image and page data that is reproduced on an output print likewise identifies a data source and processing variables. In a more general way, it should be appreciated that the same type of metadata can be useful if coupled to images in other applications. As examples, images digitally obtained via satellite or aerial apparatus, medical or industrial diagnostic images, or images from oceanographic devices often require additional metadata in order to enable correct interpretation of the image data or printing of an image using such data. Images from such devices, because these images are provided as digital data, can undergo a substantial amount of processing before such images are provided on an output print.
There are a number of conventional methods for recording metadata on RIP setup variables used to prepare a digital proof. In the simplest case, an operator may manually take notes on variable settings used. As another example, to provide metadata on the RIP setup proofing variables used to prepare a specific digital proof, and to provide other identifying information about the proof, conventional proofing systems such as the “APPROVAL PS or XP/XP4 Digital Proofing System” might record key identification and image processing variables on the proof itself, typically printed apart from the image, such as in an extreme corner of a proof sheet. Methods such as these might serve the needs of an observer viewing the proof, but would not easily allow automated methods to facilitate access of this information for display, archiving, or the like. Moreover, such handwritten or printed text message would not provide a means for positively authenticating a print as having been produced by a specific prepress system.
Conventional methods for coupling information about a printed image (that is, metadata) to an output print include providing information on an attached magnetic strip. This solution allows storage of some data, but has inherent disadvantages. For example, magnetically encoded media must be protected from magnets or strong electromagnetic fields. The task of reading information from this type of media requires placing the media, in proper orientation, into a reader device. Moreover, magnetic methods provide no easy way to identify and possibly re-use imaging system settings used for an image, such as for the remote proofing situation outlined above.
Attachment of an electronic memory component to the print substrate has inherent disadvantages when physical connection must be made to the memory component for recording or obtaining metadata stored in the memory component. Connectors add cost and present reliability problems caused by dust and dirt and repeated connection/disconnection duty cycles.
Optical encoding, such as using a bar code, is a familiar method widely used for identifying and tracking items in retail merchandising or shipping applications. Bar codes have also been used for tracking and identifying images. In diagnostic imaging, for example, patient identification information can be optically encoded directly onto a film such as for X-rays, ultrasound, or CAT (Computerized Axial Tomography) scan, as is disclosed in U.S. Pat. No. 5,288,977 (Amendolia et al.) Methods used for providing information with such a diagnostic image include encoding information on the edge of the film substrate containing the image using a bar code or other optical encoding.
Applications in photographic film processing and printing have used optical encoding in various ways for identifying negative frames and exposure conditions. For example, U.S. Pat. No. 5,905,580 (Cok et al.) discloses use of a bar code on a developed negative for frame identification. As another example, prints generated using APS advanced Photo System) technology, such as is provided with KODAK “ADVANTIX”™ film available from the Eastman Kodak Company, can include some limited information, such as date and time data printed on the reverse side of a print. However, other than back-printing of this relatively small amount of text data, other useful information is not encoded onto the print itself. U.S. Pat. No. 5,023,656 (Terashita) discloses imprinting of focus and range distance information as bar code data on the edge of a photographic film to improve negative development quality by a processor, based on this information. Again, however, this information is not provided on the output print itself.
For conventional silver-halide photoprocessing using light-exposure techniques, U.S. Pat. No. 4,951,086 (Hicks) discloses using a separate, marked photographic print having a bar-coding that includes photographic processing information to assist in ordering and processing photographic reprints. This information identifies a photographic print so that its corresponding negative can be located on a specific reel. Bar code information also provides information on exposure settings made on the photoprocessing apparatus in order to create a photographic print such as for color balance and density, and cropping adjustments. An operator can use the bar code information to improve the accuracy of reproduction of a photographic reprint or to serve as a basis for making further exposure or cropping adjustments to improve the look of a photographic reprint to suit a customer.
Bar codes have been used in verification and tracking of paper documents, as is disclosed in U.S. Pat. No. 5,671,282 (Wolff et al.) The Wolff et al. patent provides a method, using bar code or other optical encoding, for authenticating a copy of a document as valid, to help prevent forgery or prevent substitution of an incorrect document (for example, with drug prescriptions). In a similar manner, for an electronic document processing system, where paper documents and their corresponding files can be shared on a network comprising multiple authors and users and may be stored, reprinted, or photocopied on any number of devices, U.S. Pat. No. 5,486,686 (Zdybel, Jr. et al.) discloses the printing of encoded optical data on an electronic document, for purposes of authentication. To validate and qualify a paper document produced by an electronic document processing system, the Zdybel, Jr. et al. patent also discloses use of a printed optical encoding for identifying the specific machine that prints an electronic document and for listing the image rendering characteristics used by that machine.
However, a prepress proof is a different type of document than that contemplated by the Zdybel, Jr. et al. and Wolff et al. patents mentioned above. A preprocess proof is not an original; rather, it is a representation of the desired press output. The primary function of a proof is emulation of a printing press (allowing a close match to a final printed output in terms of color, printing parameters, and even paper stock “look and feel”) and its use is as an intermediate product in an overall prepress workflow. However, it would be beneficial to provide, on a prepress proof (as well as on an output image from a diagnostic or aerial photography system), some of the same types of identifying information applied to documents in the Zdybel, Jr. et al. and Wolff et al. disclosures.
Additionally, encryption of bar codes, as disclosed in U.S. Pat. No. 4,641,347 (Clark et al.), provides a method for validating the source and authenticity of an attached document to detect theft or forgery. Positive print authentication for output proofs can have particular value. It is desirable to include information on exactly bow the image is printed such that the image may be easily recreated and tracked through to the printing press. For example, during successive stages in prepress workflow, several output prints can be generated as proofs. To the unaided eye, or to someone not familiar with the detailed history of a specific print job, two proofs, each generated during a different stage, can appear to be identical. Thus it can be seen that the likelihood of confusion could be minimized if there were a convenient method for distinguishing between digital proofs produced using different setup parameters.
U.S. Pat. No. 5,724,491 (Kashihara) discloses the use of bar code optical encoding in prepress applications. In the Kashihara disclosure, a separate command sheet is used during an intermediate step in prepress workflow. The command sheet identifies the intended placement of images for a print job. A prepress operator uses the command sheet for accessing, scanning, processing, and imposing each individual image or text component used, in order to create a printing plate. Bar codes on the command sheet provide an operator with an automated method for accurate image identification and placement, such as would be required when creating a proof or a printing plate. Notably, the bar code disclosed in the Kashihara patent prints as an overlay to each image component on a separate layout paper or command sheet, intended for use by an operator when preparing printing plates. Images printed on the command sheet are not intended to emulate final printed color or appearance; rather, the images are typically at low-resolution, intended “for position only”. Moreover, any output proof generated using such a method would not include identifying information provided by these temporary bar codes. That is, metadata about the print itself, which would be useful to anyone examining the print, does not appear on the output print.
Thus, it can be seen that while there have been methods for coupling information to individual images and graphical components and for tracking and validating documents, conventional approaches are lacking in addressing the long-felt needs and specific requirements for processing, accurate analysis, and positive verification of digitally processed prints such as are provided from a digital proofing system.